As a refrigerating machine, a turbo refrigerating machine which is provided with a turbo compressor which compresses a refrigerant by rotating an impeller by an electric motor is known. In the turbo compressor, a diffuser flow path is provided around the impeller, and a refrigerant led out in a radial direction by the rotation of the impeller is pressurized in the diffuser flow path, and the pressurized refrigerant is introduced into a scroll flow path. The diffuser flow path is provided in a casing and smoothly communicates with a hub of the impeller (refer to, for example, Patent Document 1).
Patent Document 2 discloses a collecting port which is provided by machining a portion of the casing configuring the diffuser flow path and the scroll flow path in a gas turbine engine having a centrifugal compressor and captures foreign matter contained in the air that is a working fluid. The collecting port is formed in an endmost portion in a radial direction of the diffuser flow path (refer to Paragraphs [0017] and [0018] and FIGS. 1 and 2 of Patent Document 2).
Patent Document 3 discloses a configuration in which in a centrifugal compressor which compresses gas, foreign matter contained in the gas is prevented from infiltrating into the back surface of the impeller by supplying buffer gas to the back surface of the impeller and causing the buffer gas to flow through the gap between the back surface of the impeller formed in a smooth surface and the casing toward the outside in a radial direction of the back surface of the impeller. The buffer gas flows through the gap and joins a main stream of the gas flowing through a diffuser flow path from a gap 4a between an outer periphery 1c of the impeller and the casing (refer to Abstract and FIGS. 1 and 2 of Patent Document 3).
Patent Document 4 discloses a configuration in which in a turbo refrigerating machine provided with a turbo compressor, a first impeller and a second impeller are fixed to a rotating shaft and the rotating shaft is supported on a bearing (from Abstract of Patent Document 4).